Production of hydrocarbons from loose, unconsolidated, and/or fractured formations often produces large volumes of particulates along with the formation fluids. These particulates can cause a variety of problems. For this reason, operators use gravel packing as a common technique for controlling the production of such particulates.
To gravel pack or fracture pack a completion, a screen is lowered on a workstring into the wellbore and is placed adjacent the subterranean formation or in perforated casing. Proppant, sand, or particulate material (collectively referred to as “gravel”) and a carrier fluid are pumped as a slurry down the workstring. Eventually, the slurry can exit through a “cross-over” into the wellbore annulus formed between the screen and the wellbore.
The carrier liquid in the slurry normally flows into the formation and/or through the screen itself. However, the screen is sized to prevent the gravel from flowing through the screen. This results in the gravel being deposited or “screened out” in the annulus between the screen and the wellbore to form a gravel-pack around the screen. The gravel, in turn, is sized so that it forms a permeable mass (i.e., a gravel pack) that allows produced fluids to flow through the mass and into the screen but blocks the flow of particulates into the screen.
Due to poor distribution, it is often difficult to completely pack the entire length of the wellbore annulus around the screen, which may lead to an interval in the annulus being incompletely packed with gravel. This poor distribution of gravel is often caused by the carrier liquid in the slurry being lost to the more permeable portions of the formation. Due to the loss of the carrier liquid, the gravel in the slurry forms “sand bridges” in the annulus before all of the gravel has been placed around the screen. Such bridges block further flow of the slurry through the annulus, thereby preventing the placement of sufficient gravel below the bridge in top-to-bottom packing operations or above the bridge in bottom-to-top packing operations.
Alternate flow conduits, called shunt tubes, can alleviate this bridging problem by providing a flow path for the slurry around such sections that tend to form sand bridges. The shunt tubes are typically run along the length of the wellscreen and are attached to the screen by welds. Once the screen assemblies are joined, fluid continuity between the shunt tubes on adjacent screen assemblies must be provided, and several techniques have been developed to provide such continuity.
FIGS. 1A-1B are schematic views of examples of sand screens 18a-b provided with shunt tubes 30a-b of a wellscreen assembly 10. FIG. 1C illustrates an exploded view of the components for the wellscreen assembly 10 for use in an open hole. As an alternative, FIG. 2 illustrates an exploded view of components for the wellscreen assembly 10 for use in a cased hole.
In the assembly 10, a first sand control device 12a is coupled to a second sand control device 12b, and each device 12a-b has basepipe joints 14 joined together to define a production bore 16. Screens 18a-b having filter media surround the basepipe joints 14 and are supported by ribs 19. The assembly 10 is provided with shunt tubes 30a-b, which in this example are steel tubes having substantially rectangular cross-section. The shunt tubes 30a-b are supported on the exterior of the screens 18a-b and provide an alternate flow path 32.
To provide fluid communication between the adjacent sand control devices 12a-b, jumper tubes 40 are disposed between the shunt tubes 30a-b. In this way, the shunt tubes 30a-b and the jumper tubes 40 maintain the flow path 32 outside the length of the assembly 10, even if the borehole's annular space B is bridged, for example, by a loss of integrity in a part of the formation F.
Additional examples of shunt tube arrangements can be found in U.S. Pat. Nos. 4,945,991 and 5,113,935. The shunt tubes may also be internal to the filter media, as described in U.S. Pat. Nos. 5,515,915 and 6,227,303.
As shown in FIGS. 1A-1C, the assembly 10 for an open hole completion typically has main shrouds 28a-b that extend completely over the sand control devices 12a-b and provides a protective sleeve for the filter media and shunt tubes 30a-b. The shrouds 28a-b have apertures to allow for fluid flow. The main shrouds 28a-b terminate at the end rings 20a-b, which supports ends of the shrouds 28a-b and have passages for the ends of the shunt tubes 30a-b. For a cased hole completion, the assembly 10 as shown in FIG. 2 may lack shrouds.
Either way, the shunt tubes 30a-b stop a certain length from the ends of the sand control devices 12a-b to allow handling room when the devices 12a-b are joined together at the rig. Once the devices 12a-b are joined, their respective shunt tubes 30a-b are linearly aligned, but there is still a gap between them. Continuity of the shunt tubes' flow path 32 is typically established by installing the short, pre-sized jumper tubes 40 in the gap.
Each jumper tube 40 has a connector 50 at each end that contains a set of seals and is designed to slide onto the end of the jumper tube 40 in a telescoping engagement. When the jumper tube 40 is installed into the gap between the shunt tubes 30a-b, the connectors 50 are driven partially off the end of the jumper tube 40 and onto the ends of the shunt tube 30a-b until the connectors 50 are in a sealing engagement with both shunt tubes 30a-b and the jumper tube 40. The shunt tubes' flow path 32 is established once both connectors 50 are in place. A series of set screws (not shown) can engage both the jumper tube 40 and adjoining shunt tube 30a-b. The screws are driven against the tube surfaces, providing a friction lock to secure the connector 50 in place.
This connection may not be very secure, and there is concern that debris or protruding surfaces of the wellbore can dislodge the connectors 50 from sealing engagement with the tubes 30a-b and 40 while running the wellscreen assembly 10 into the wellbore. Therefore, a device called a split cover 22 as shown in FIG. 1A is typically used to protect the connectors 50. The split cover 22 is a piece of thin-gauge perforated tube, essentially the same diameter as the main shrouds 28a-b of the screen assembly 10, and the same length as the gap between the end rings 20a-b. The perforated cover 22 is spit into halves with longitudinal cuts, and the halves are rejoined with hinges along one seam and with locking nut and bolt arrangements along the other seam. The split cover 22 can be opened, wrapped around the gap area between the sand control devices 12a-b, and then closed and secured with the locking bolts.
Typically, the split cover 22 is perforated with large openings that do not inhibit movement of the gravel and slurry. Primarily, the split cover 22 acts as a protective shroud so that the assembly 10 does not get hung up on the end rings 20a-b when running in hole or so the jumper tubes 40, connectors 50, and shunt tubes 30a-b are not damaged during run in.
As can be seen above, proppant or gravel in gravel pack or frac pack operations is placed along the length of a sand face completion whether it is open hole or cased hole. To place the gravel in a gravel pack operation, the carrier fluid carries the gravel to the sand face to pack the void space between the sand face and the sand screen. In a frac pack operation, the carrier fluid carriers the gravel to fracture the reservoir rock and to increase the sand face/gravel contact area. Then, the annular space is packed with the gravel between the cased or open hole and the sand screen.
To leave a fully supported gravel pack in the annulus, the carrier fluid dehydrates and leaves the gravel in a fully supported position. Depending on the operation, dehydration occurs through the reservoir sand face into the reservoir and/or through the sand screens 18a-b and up the wellbore 16. When fluid dehydrates through the sand screens 18a-b, there must be an adequate open area that provides access to flow paths allowing the carrier fluid to return up the well.
Most sand screen assemblies 10 have blank areas or gaps near the basepipe connections 15 where the sand screens 18a-b are made up when running in hole. These blank areas on the sand screen assemblies provide no open area for fluid dehydration. Consequently, gravel pack settling is unstable in these blank areas, creating unstable pack sections around the sand screens' blank area having voids or space. Gravel that has been packed uphole or downhole might eventually migrate or shift due to fluid flow and gravity. This shifting can expose sections of the screen and may lead to a loss of sand control.
These blank areas on sand screens with shunt tubes made for open hole gravel packs are further isolated by a large top ring of the lower joint and a larger bottom ring of the upper joint. The top and bottom rings support the transport and shunt tubes, but provide no open area for fluid dehydration. As a consequence, the top and bottom end rings can make the gravel pack settling in the blank area even more unstable. In fact, these unstable pack sections around the sand screen blank area provide voids or spaces that gravel from above might eventually migrate or shift due to fluid flow and gravity. This shifting creates exposed screen sections, which might lead to a loss of sand control.
For cased hole systems, it has often been assumed that gravity will cause the gravel to settle along the blank area and dehydrate below to the lower screen. For this reason, cased hole shunt tube systems may be less concerned with dehydrating the blank area. In open hole horizontal gravel pack with shunt tubes, however, a leak-off tube may be placed across each connection to provide a flow path up to the immediate screen above the connection. The fluid exits the leak-off tube and enters through the screen, passes then into the basepipe, and finally returns to the surface.
During gravel packing of the assemblies of FIGS. 1A-1C and 2, for example, gravel slurry can readily communicate around the blank area between the end rings 20a-b on the basepipes 14. For example, the slurry can readily enter through the shroud 22 and can collect in the blank area between the top and bottom end rings 20a-b around the basepipes 14. The slurry becomes trapped in the blank area because the gravel cannot dehydrate and the carrier fluid cannot return uphole. To deal with this, a leak-off tube 34 can be positioned in this blank area between the top and bottom end rings 20a-b. The leak-off tube 34 has openings (not shown) along it that allow the carrier fluid to enter from the slurry in the blank area so the gravel can dehydrate.
Although the leak-off tube may be effective to an extent to dehydrate slurry in the blank area, better distribution of gravel is desired in both open and cased holes to improve sand control. To that end, the subject matter of the present disclosure is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.